Constraining the global composition of D/H and 18O/16O in Martian water using SOFIA/EXES

• Published in: Monthly Notices of the Royal Astronomical Society
• Main Authors: Alday, Juan, Aoki, S., Dewitt, C., Montmessin, Franck, Holmes, J. A., Patel, M. R., Mason, J. P., Encrenaz, T., Richter, M. J., Irwin, P. G.J., Daerden, F., Terada, N., Nakagawa, H.
• Other Authors: Graduate School of Frontier Sciences Kashiwa, The University of Tokyo (UTokyo), School of Physical Sciences Milton Keynes, Faculty of Science, Technology, Engineering and Mathematics Milton Keynes, The Open University Milton Keynes (OU)-The Open University Milton Keynes (OU), Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique (BIRA-IASB), NASA Ames Research Center (ARC), Space Science Institute Boulder (SSI), PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Sorbonne Université (SU), Department of Physics and Astronomy Univ California Davis (Physics - UC Davis), University of California Davis (UC Davis), University of California (UC)-University of California (UC), Department of Atmospheric, Oceanic and Planetary Physics Oxford (AOPP), University of Oxford, Graduate School of Science Sendai, Tohoku University Sendai, Universität Stuttgart, UK Space Agency, Universities Space Research Association, Deutsches Zentrum für Luft- und Raumfahrt, Japan Society for the Promotion of Science, National Aeronautics and Space Administration, Science and Technology Facilities Council
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2024
• Subjects: planets; planets and satellites: atmospheres; radiative transfer; satellites: terrestrial planets; [SDU]Sciences of the Universe [physics]; Ice cap
• Online Access: https://hal.science/hal-04616687; https://hal.science/hal-04616687/document; https://hal.science/hal-04616687/file/stae1067.pdf; https://doi.org/10.1093/mnras/stae1067

International audience Isotopic ratios in water vapour carry important information about the water reservoir on Mars. Localized variations in these ratios can inform us about the water cycle and surfaceu2013atmosphere exchanges. On the other hand, the global isotopic composition of the atmosphere carries the imprints of the long-term fractionation, providing crucial information about the early water reservoir and its evolution throughout history. Here, we report the analysis of measurements of the D/H and 18O/16O isotopic ratios in water vapour in different seasons (LS = 15◦, 127◦, 272◦, and 305◦) made with the Echelon-Cross-Echelle Spectrograph (EXES) aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). These measurements, free of telluric absorption, provide a unique tool for constraining the global isotopic composition of Martian water vapour. We find the maximum planetary D/H ratio in our observations during the northern summer (D/H = 5.2 ± 0.2 with respect to the Vienna Standard Mean Ocean Water, VSMOW) and to exhibit relatively small variations throughout the year (D/H = 5.0 ± 0.2 and 4.3 ± 0.4 VSMOW during the northern winter and spring, respectively), which are to first order consistent though noticeably larger than the expectations from condensation-induced fractionation. Our measurements reveal the annually averaged isotopic composition of water vapour to be consistent with D/H = 5.0 ± 0.2 and 18 O/ 16 O = 1.09 ± 0.08 VSMOW. In addition, based on a comparison between the SOFIA/EXES measurements and the predictions from a Global Climate Model, we estimate the D/H in the northern polar ice cap to be ∼5 per cent larger than that in the atmospheric reservoir (D/Hice = 5.3 ± 0.3 VSMOW).